1. Field of the Invention
This invention relates to an optical information recording and/or reproducing apparatus wherein an access to an objective track can be made within a short time.
2. Related Art Statement
There is recently noted an optical information recording and/or reproducing apparatus wherein information is recorded at a high density or information recorded at a high density is quickly reproduced by converging and radiating a light beam onto an optical recording medium (disc) instead of using a magnetic head.
In the above mentioned optical apparatus, generally a track access means is provided so as to be able to record information in any objective track or to reproduce information from any objective track. Also, a focusing servo-means is provided so that the light beam radiated onto the disc may be in the form of a spot and a tracking servo-means is provided so as to hold the light beam on a predetermined track.
Now, the above mentioned track access means is made by using a coarse access (coarsely moving) means moving an optical head (pickup) containing an optical system including such optical means of converging and radiating a light beam onto a disc as, for example, an objective lens in the radial direction of the disc by means of a voice coil motor or the like and a fine access (finely moving) means moving the objective lens of the optical head by means of a lens actuator so that the coarse access means or fine access means may be operated in response to the size from the present track position. The access process wherein the optical head is moved near to the objective track by the above mentioned coarse access means within a short time and the objective lens is finely moved to be mounted on the objective track is general. However, in the case of the movement of the optical head by the coarse access means and the following stop, a force in the direction reverse to the direction of the force acting on the optical head will act on the objective lens so that the objective lens will be vibrated into the radial direction of the disc by the resilient members supporting it. If the objective lens is thus vibrated, in case the objective lens is subsequently finely moved to approach the objective track, the track will not be able to be accurately approached. Therefore, a fine access will be made only after the vibration becomes small enough. In this manner, there is a defect that the track access takes time.
In order to solve the above mentioned problem, for example, there are two related art examples as in the following.
In the first related art example disclosed in the Patent Gazette of Japanese Patent Laid Open No. 94940/1982, in making a coarse access by having an electric current flow through a voice coil motor. The current also flows through a tracking coil (lens actuator) to prevent the objective lens from vibrating in case the optical head is moved.
In the second related art example disclosed in the Patent Gazette of Japanese Patent Laid Open No. 193553/1984, a coarse access is made when the objective lens is positioned in a fixed position of the base of the optical head to prevent the objective lens from vibrating.
In either of the above mentioned first and second related art examples, no effective measures are taken or no effective means are disclosed to effectively prevent the objective lens from vibrating when the coarse access ends.
That is to say, in case the coarse access ends, the electric current flowing to the voice coil motor will become zero. However, at this time the objective lens will hold the inertia when it is moved, and will be therefore swung in the reverse direction to the direction of starting and will be vibrated. In this case, even if a part of the voltage applied to the voice coil motor at the time of the coarse access is applied also on the actuator coil and the current is made zero by a timing synchronized with the voice coil motor side when the coarse access ends, for example, the objective lens will not be able to be said to move as perfectly synchronized without any time delay with the movement of the optical head and will continue to vibrate.
When the coarse access ends, it will be necessary to read out the track position at that time point. Therefore, in case the objective lens is clamped and held until then so as to be mounted on the track, the tracking servo-means will have to be operated after releasing the clamping. However, in this case, in order to prevent the influence of the eccentricity or the like of the disc, a two-step servo-state may be set making the voice coil motor side also movable. In such a two-step servo-state, the objective lens will be vibrated particularly by the movement of the voice coil.